The present invention relates to a copying machine or printer incorporating a plurality of developing devices.
To meet the requirement for multi-color copying, copying machines have been proposed in recent years which have a plurality of developing devices provided around a photosensitive drum and adjacent thereto. The copying machine develops an electrostatic latent image in one of various colors with one of the developing devices selectively driven.
However, the above copying machine has the problem that the surface potential of the photosensitive member differs at the positions opposed to the developing devices. This is because the different developing devices require different periods of time to rotate from charging position to developing position.
The difference in the surface potential due to the difference in the developing position gives rise to a difference in the image density of copy images developed by the developing devices even if the same original is copied. The above phenomenon appears attributable to the difference between the developing positions in the developing voltage (which is the difference between the developing potential applied to the developing device and the surface potential of the photosensitive member).